A three-dimensional simulation of transient natural convection in a triangular cavity (original) (raw)
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2015
The two-dimensional laminar natural convective transient flow characteristics in a differentially heated air-filled tall cavity with gradual heating are investigated both experimentally and numerically for various parameters such as Rayleigh number and temperature difference. Experimental computations are performed for temperature difference varying from (∆T = 5°C) to (∆T = 23°C) while the Rayleigh number varies from (Ra = 2929) to (Ra =11772) to cover a wide range of the flow field inside the cavity. The results show that as the Rayleigh number increases the flow becomes unstable. Also, the flow characteristics are observed to be multi-cellular and time variant especially at high Rayleigh numbers. Moreover, numerical computations are performed to compare with the experimental results.
Numerical Computation of Laminar Natural Convection in Triangular Shaped Cavities
2020
In the present work, a numerical analysis of laminar natural convection in right and isosceles triangular enclosures has been carried out. Two dimensional, steady-state governing equations (conservation of mass, momentum and energy) were solved in Cartesian coordinates by the finite volume method. Several configurations are examined over a range of Rayleigh numbers that ranged from 103 to 105; for cavity walls that are heated, cooled or insulated. Streamlines and isotherms are displayed as streamline plots and isotherm lines for various triangular enclosures and, for Rayleigh number ranged from 103 to 105 with heated from the bottom. The effect of the aspect ratio, that is taken as a parameter, on the convective flow and isothermal contours in the triangular cavity are examined in detail. Symmetry breaking pitchfork bifurcations and multicellular flow structures and their effects on temperature distributions at low aspect ratios and high Rayleigh numbers are inspected. The overall h...
An experimental study of transient natural convection in a side-cooled cavity
2008
Transient natural convection in a side-cooled cavity is experimentally investigated. The shadowgraph technique is used to visualize the flow in the cavity. The results indicate that the flow development is characterized by the following distinct processes: (a) the initial growth of the vertical thermal boundary layers and horizontal intrusions; (b) the interaction of the intrusions and filling up of the cavity; and (c) the stratification and formation of double layer structures.
Unsteady natural convection in a triangular enclosure under isothermal heating
The fluid flow and heat transfer inside a triangular enclosure due to instantaneous heating on the inclined walls are investigated using an improved scaling analysis and direct numerical simulations. The development of the unsteady natural convection boundary layer under the inclined walls may be classified into three distinct stages including a start-up stage, a transitional stage and a steady state stage, which can be clearly identified in the analytical and numerical results. A new triple-layer integral approach of scaling analysis has been considered to obtain major scaling relations of the velocity, thicknesses, Nusselt number and the flow development time of the natural convection boundary layer and verified by direct numerical simulations over a wide range of flow parameters.
Simulation of Natural Convection in a Square Cavity with Partially Heated and Cooled Vertical Walls
Proceeding of 5th Thermal and Fluids Engineering Conference (TFEC)
Natural convection driven by temperature differences between partially heated and cooled vertical walls in a square cavity is studied numerically. Steady or unsteady cellular flow structures and temperature patterns are illustrated along with the evolution of heat transfer rates in terms of Nusselt number. The cavity is filled with fluids of various Prandtl number, including .024 (liquid metal), .71 (air), 6 (water), and 450 (silicon oil). The effect of Prandtl and Rayleigh numbers on the flow regime and heat transfer is established along with two different thermal boundary conditions.
Natural convection in a rectangular cavity with wall temperature decreasing at a uniform rate
W�rme - und Stoff�bertragung, 1982
The transient natural convection in a fluid contained in a rectangular enclosure, the wall of which is maintained at a uniform temperature which changes at a steady rate, is approached by a numerical method. Numerical solutions are obtained for Pr = 0.73, 7.3 and 73 and a range of Rayleigh numbers Ra = 102 ~ l0 s. At relatively low Rayleigh numbers the flow is characterized by the development of double cells with flow up the center and down the sidewalls. However it was found that an increase of the Rayleigh number leads to the development of strong secondary circulation on the axis of symmetry of the cavity near the top wall. Thus, as the Rayleigh number is increased the secondary cells grow in size. The effects of the secondary cells on the temperature field and heat transfer coefficients are discussed. Most results are obtained for the case of a square cavity (E ~-2) but the influence of the aspect ratio of the cavity is also studied for E = 1 and 4. Freie Konvektion in reehtwinkeligen Riiumen bei mit der Zeit linear fallenden Wandtemperaturen
Effects of heating intensity on the transient natural convection flows in open cavities
The effects of the air variable properties (density, viscosity and thermal conductivity) on the transient buoyancy-driven flows established in open square cavities are investigated. Two-dimensional, laminar, transitional and turbulent simulations are obtained, mainly considering uniform heat flux heating conditions. For the fully understanding of the transient flow, different configurations are considered, including those chosen for comparison purposes. The low-Reynolds k-x turbulence model is employed. The average Nusselt number and the dimensionless mass-flow rate have been obtained for a wide range of the Rayleigh number varying from 10 5 to 10 12 . The changes produced along the time in the flow patterns inside the cavity when the effects of variation of properties are relevant, are also shown. The transient evolution of the flow is strongly affected when the heating parameter is high enough.
IOP Conference Series: Materials Science and Engineering, 2019
Effects of cavity aspect ratios and cavity inclination angles to natural convection in a rectangular cavity are numerically investigated. Investigation is performed at the Rayleigh number (Ra) equal to 104, the cavity aspect ratios from 1 to 50 and the cavity inclination angles from 0 to 180°. Consequently, Heat transfer enhancement or decreasing due to the effects is exposed. In addition, streamline contours in the rectangular cavity are illustrated. Multi-cellular flow figuring on the appropriate conditions is exhibited. A new correlation of the average Nusselt number, the cavity aspect ratio and the cavity inclination angle is formulated at Ra equal to 104.
Numerical Study of Natural Convection Inside a Square Cavity with Non-uniform Heating from Top
Journal of The Institution of Engineers (India): Series C, 2020
The prime objective of the present numerical study is to analyse buoyancy-driven thermal flow behaviour inside an enclosure with the application of nonlinear heating from top surface which is commonly essential in glass industries. A fluid-filled square cavity with sinusoidal heating from top surface, adiabatic bottom wall and constant temperature side walls is considered here. The thermal flow behaviour has been numerically observed with the help of relevant parameters like stream functions, isotherms and Nusselt number. For the present investigation, Rayleigh number (Ra), Prandtl number (Pr) and heating frequency of the wall (x) are varied from 10 3 to 10 6 , 0.7 to 7 and 0.5 to 2, respectively. It has been noticed from the investigation that flow dynamics drastically alter with Ra, x and Pr. However, the effect of Ra on heat transfer rate has been found to be significantly higher while compared with the influences by x and Pr. Keywords Free convection Á Buoyancy Á Rayleigh number Á Pr number Á Sinusoidal heating Greek letters a Thermal diffusivity (m 2 s-1) b Volumetric expansion coefficient (K-1) q Kinetic viscosity (m 2 s-1) t Density of fluid (kg m-3) h Dimensionless temperature x Heating frequency of the top wall
2013
A numerical study is performed to analyze the steady natural convection phenomena of air in a square cavity with different locations of the heating portion. The heat sources parts in the left, right and bottom walls of the cavity are maintained at a higher temperature Th, whereas the other parts of these sidewalls are kept at a lower temperature Tc. The enclosure’s top wall is kept insulated. The coupled equations of continuity, momentum and energy are solved by a finite volume method. The SIMPLE algorithm is used to solve iteratively the pressurevelocities coupling. The numerical investigations in this analysis is made over a wide range of parameters, Rayleigh number ( ) and dimensionless heater lengths. The effect of three different heating locations on the vertical walls (bottom, Centre, and top) and the local heat source on the bottom wall was evaluated. Results are presented graphically in the form of streamlines, isotherms and also with a velocity profiles and average Nusselt ...